The present invention relates to the production of useful organic products from diverse biomass. In particular, the invention relates to the large-scale production of organic products such as sugars, ethanol, lignan and derivative biodegradable thermoplastics from agricultural, forestry and municipal wastes, in an energy efficient and environmentally sensitive manner.
Mixed municipal solid waste (MSW) typically constitutes about two-thirds organic biomass materials and is rarely disposed other than by costly, environmentally polluting incineration or landfilling. A widespread approach to partially reducing the volume of cellulosic solid wastes going into landfill is through composting, particularly of source separated xe2x80x9cgreenwastexe2x80x9d that includes yard waste, vegetable material and mixed waste paper. Composting involves natural aerobic fermentation under the action of bacteria, yeast and fungal organisms and their enzymes that in commercial practice degrade principally the carbohydrate and hemicellulose polysaccharide components of biomass. The result is a volume reduction by about one-third of solid waste and a comparatively low-value, highly cellulosic, water-shedding residue, marketed as a soil amendmentxe2x80x94xe2x80x9ccompost.xe2x80x9d The value of this product rarely pays the cost of disposal, and the substantial tipping fee-subsidized market often involves negative revenue to transport for spreading on agricultural lands or landfill incorporation.
Many attempts have been made to improve upon existing biomass processing techniques in order to improve the efficiency of processing and the yield of useful organic materials obtained.
U.S. Pat. No. 4,110,281 to Dreer is directed toward producing a variety of value-added material products as an alternative to low-value disposal. Dreer describes a process for reducing MSW to compost in which the MSW is ground, extracted of metal and further chemically processed with organic solvents and resin.
U.S. Pat. No. 5,326,477 to Fuqua et al. describes a process directed toward volume reduction and sewage disposal of certain high cellulose content solid waste, such as disposable diapers and pads, by liquefaction through enzymatic breakdown in a cellulase solution. The process conditions given are such as to support rapid, partial fragmentation of the cellulosic polymer chains sufficient to render the material suitable for liquid transportable discharge through a pipe. Provision is made to capture a plastic shell (film) for prospective recycling.
U.S. Pat. No. 5,705,216 to Tyson discloses methods of alkaline pulping using a mechanical extruder to crush and feed NaOH-soaked biomass wastes, such as wood and agricultural residues, into a pressure chamber where, under the action of saturated steam in the 200xc2x0 C. regime, the material is digested for several minutes. Tyson""s process is terminated by sudden pressure release (steam explosion) on the digested material as it exits the extruder. The process, with variants, is directed to the partial solubilization of lignin and hemicellulose and the disruption of the lignocellulosic matrix of biomass with the principal purpose of creating a reactive, absorbent, fibrous material. This product aims to serve a variety of purposes from ruminant animal feed to composite alternative structural materials (with or without the addition of recycled thermoplastics). Another aim of the invention is to extract from the treated fiber a solubilized portion of the polymeric constituents lignin and hemicellulose, together comprising an extractable weight reduction of about 32% of the feedstock material. Typically, hemicellulose and lignin together comprise about 50% of biomass feedstock materials. In Tyson""s process, the extracted portion of the hemicellulose is optionally available to subsequent enzymatic hydrolysis to sugars with prospective fermentation to ethanol and organic acids.
Alternatively, U.S. Pat. No. 4,728,367 to Huber describes an extruder device and a process for either strong or dilute acid pretreatment directed toward providing partial solubilization and hydrolysis of hemicellulose from lignocellulosic materials. Under comparatively elevated temperatures and pressures and very short acid contact times of several seconds, Huber indicates glucose production of a modest 13-20% of feedstock.
Another approach to biomass chemical decomposition directed toward sugar production for subsequent fermentation to ethanol has been described in the U.S. Pat. No. 5,221,357 to Brink. The Brink patent gives a two-stage dilute acid hydrolysis process preferably with nitric acid and carried out under saturated steam in a pressure reactor. The first stage hydrolysis is performed under comparatively mild conditions of pH (about 2), temperature (about 185xc2x0 C.) and pressure (about 10 atmospheres). The aim of the first stage is to solubilize, hydrolyze and extract most of the hemicellulose from the lignocellulosic matrix while not substantially degrading the cellulose and liberated monomeric sugars. This aim is achieved in several minutes digestion time with the result of solubilizing and enabling the extraction of about 30% of the biomass feedstock material, leaving lignin and much of the cellulose intact.
After acting to separate the solubilized five- and six-carbon sugars of the hemicellulose, the Brink process then addresses the more difficult issue of hydrolysis and solubilization of the cellulose polysaccharide under more extreme conditions of lower pH, temperature over 200xc2x0 C. and pressure 20 atmospheres for over 10 minutes. Under carefully tailored conditions for a given homogeneous feedstock, sugar production and degradation can be optimized to yield a total about 60% of potential sugars in the two-stage dilute acid process.
Other innovations the Brink process introduces are, first, solvent extraction of high-boiling-point coproduct chemicalsxe2x80x94particularly furfural and acetic acidxe2x80x94from the sugar-containing liquid hydrolysate of the first stage before fermentation. Second, the process incorporates mechanical refinement of the first stage pretreated solids in a device (described in U.S. Pat. No. 4,206,903 to Brink).
An additional disruptive process for terminating the first stage in a steam explosion decompression through a decompression orifice is disclosed in subsequent Pat. No. 5,628,830 to Brink (""830 patent). The patent describes an alternative process directed toward increasing sugar and ethanol yield through a second hydrolysis of the lignocellulosic solids from the first stage by enzymatic digestion. Relative to Brink""s ""903 patent, his enzymatic process replaces the second stage dilute acid hydrolysis of cellulose under more severe conditions than the first stage hydrolysis of hemicellulose. The ""830 patent reveals that, with the combined mechanical refinement and steam explosion disintegration, a preponderance of the solid particles is smaller than about 100 mesh for typical woody substrates. Further, the ""830 patent description reveals that, at cellulase enzyme loading of about 13.5 FPU/gm on mixed New York hardwood substrate, at low, and with about 5% solids loading in aqueous carrier, the process-implemented batch simultaneous saccharification and fermentation (SSF) with S. cereviseae yeast is capable to yield 89.2% cellulose-to-ethanol conversion in 4 days. One of skill in the art will understand that the combination of low solids loading and SSF fermentation act together to limit buildup of sugar concentrations in the reactor and contain so-called end product inhibition of enzymatic hydrolysis. Accordingly, Brink""s results indicate a significant speedup in batch enzymatic hydrolysis of dilute acid pretreated lignocellulose solids substrate vis-à-vis the comparative literature, heretofore.
Adding the fermentation of extracted sugars from first dilute acid hydrolysate using the five- and six-carbon sugar metabolizing organism Pitchia stipititis, Brink further reveals capability for a total ethanol yield from the combined process of 561 lb/ton or 85 gal/ton feedstock.
In another technology advance, U.S. Pat. No. 5,036,005 to Tedder describes an invention directed toward efficient, continuous fermentation of sugars with continuous solvent extraction of both ethanol and volatile organic coproducts from a biocatalyst-containing fermentation broth. The invention poses the opportunity to economically recover volatile organic coproducts and ethanol with low expenditure of energy and capital cost, while also avoiding additional investment in drying to fuel grade ethanol. The tightly integrated system requires the use of a solvent that conventionally has a higher boiling point than the products to be extracted and also is nontoxic to the fermentation organisms the solvent intimately contacts. The latter constraint obviates the use of otherwise attractive higher alcohols as solvents.
Despite these efforts, the extent productization and yields from biomass processing, particularly from biomass with a significant lignocellulostic component, remain relatively low or are achieved at uneconomic expenditure of time, process volumes and expensive catalysts. Cost-effective large-scale biomass processing techniques are lacking. While previous approaches have advanced the understanding of biomass processing and its yields, improved biomass processing techniques and systems would be desirable.
The present invention achieves further advances in biomass processing by providing processes and systems for the increased production of useful organic products from diverse lignocellulose-containing biomass. In particular, the present invention integrates dilute acid hydrolysis and alkaline delignification techniques in processes that enhance the quantity of products, i.e., material utilization efficiency and yield, of lignocellulostic biomass processing and enable the economic production lignin-based biodegradable plastics and other useful organic products.
The invention integrates technologies in chemical processing to achieve exceptional product yields, value added and productivity in the production of sugars, ethanol, lignin, other (photosynthetically) plant-derived organic chemicals, and process-derived biocatalyst proteins from a diverse spectrum of commonly occurring biomass sources. These prominently include wastes (residues) of agricultural, forest/mill and municipal origin. Synergistically sharing process costs while supporting (maximizing) added value in multiple products, the invention poses the prospect to newly render highly cost-effective the large-scale remanufacture (reuse) of the organic products of human activities.
Processes in accordance with the present invention may also prominently feature environmentally benign attributes of energy efficiency, material (e.g., water) conservation and avoids chemical nuisance/toxicity, which, together with the theme of renewable materials products, contribute to the objectives of sustainable ecology.
In one aspect, the present invention provides a method of processing a lignocellulose-containing biomass material. The method involves treating the biomass material by dilute acid hydrolysis and treating an unreacted lignocellulostic component of the acid hydrolyzed biomass material by alkaline delignification. In many implementations of the invention, these processing techniques will be combined with others to provide for efficient, high-yield processing of lignocellulostic biomass. Other aspects of the invention also provide systems configured for processing a lignocellulose-containing biomass material in accordance with the method of the present invention.
These and other features of the invention will be further described and exemplified in the drawings and detailed description below.